1. Technical Field
The present invention relates to a data access method and a data access device for making an access to a recording medium in order to write data into the recording medium having a real data area formed from a plurality of clusters and a management table formed from a plurality of entries showing a usage state of corresponding clusters.
2. Related Art
Many electronic devices that are currently available in the market; for instance, digital audio equipment, a digital camera, a personal computer, or the like, are equipped with a recording medium for recording and holding data. Data recorded in such a recording medium is usually managed in accordance with a previously-defined file system; for instance, an FAT file system. In such a file system, the recording medium is usually coarsely divided into a real data area where real data are recorded and a management area where data for data management are recorded. The management area is provided with a table showing usage conditions of the real data area; for instance, a File Allocation Table (FAT). When new data are written into the recording medium, a data access unit provided in an electronic device locates the position of a data writable area; namely, a so-called free storage area, by reference to the FAT.
Incidentally, a time involved in location of the position of a free storage area recently increases along with an increase in the capacity of a recording medium, which in turn raises a problem of an increase in data write processing time. Such an increase in data write processing time raises a big problem in a system requiring real-time data write operation.
Accordingly, there have been some proposals of creation and utilization of a bitmap showing a usage condition of a real data area in order to quickly locate the position of a free storage area (for instance, JP 8-221317 A, and so forth). More specifically, a real data area is divided into a plurality of blocks, thereby preparing a map that represents an assigned or unassigned state of each of the blocks by means of bit values. It has been proposed to hold the bitmap in main memory and make a reference to the bitmap as necessary. The main memory can make a faster access than does the recording medium. Therefore, according to the method for holding the bitmap in the main memory, the position of a free storage area can be quickly located.
Although main memory enables making of a high-speed access, the main memory is very smaller than the recording medium in terms of capacity. When a bitmap is held in such small-capacity main memory, a memory space for implementing processing pertaining to various processes cannot be sufficiently assured, which may adversely affect system processing. In particularly, in the case of a portable electronic device; for instance, a portable audio device, and the like, the capacity of the main memory is often comparatively small. Therefore, the problem noticeably appears.
Therefore, the present invention provides a data access method and a data access device that enable high-speed writing of data without affecting system processing.